Ratatui - a more structured way to handle state

• In this example we a struct, arbitrarily named App to repreent the state of the program. It will hold the text to be displayed and a flag indicating if we need to exit the program.
• We also separated the draw and the handle_key_event methods and moved the run method into the struct.
• We also implemented the Widget. Later we'll use a lot more widgets to improve the look of the application.

[package]
name = "hello-world"
version = "0.1.0"
edition = "2021"

[dependencies]
crossterm = "0.28.1"
ratatui = "0.29.0"

use std::io;

use crossterm::event::KeyModifiers;
use ratatui::{
    buffer::Buffer,
    crossterm::event::{self, KeyCode, KeyEventKind},
    layout::Rect,
    style::Stylize,
    widgets::{Paragraph, Widget},
    DefaultTerminal, Frame,
};

#[derive(Debug, Default)]
struct App {
    text: String,
    exit: bool,
}

impl App {
    fn run(&mut self, terminal: &mut DefaultTerminal) -> io::Result<()> {
        while !self.exit {
            terminal.draw(|frame| self.draw(frame))?;

            if let event::Event::Key(key) = event::read()? {
                self.handle_key_event(key);
            }
        }
        Ok(())
    }

    fn draw(&self, frame: &mut Frame<'_>) {
        frame.render_widget(self, frame.area());
    }

    fn handle_key_event(&mut self, key: event::KeyEvent) {
        if key.kind == KeyEventKind::Press {
            match key.code {
                KeyCode::Esc => self.exit = true,
                KeyCode::Char('c') if key.modifiers == KeyModifiers::CONTROL => self.exit = true,
                _ => self.text = format!("{} - {}", key.modifiers, key.code),
            }
        }
    }
}

impl Widget for &App {
    fn render(self, area: Rect, buf: &mut Buffer) {
        Paragraph::new(self.text.clone())
            .white()
            .on_blue()
            .render(area, buf);
    }
}

fn main() -> io::Result<()> {
    let mut terminal = ratatui::init();
    terminal.clear()?;
    let app_result = App::default().run(&mut terminal);
    ratatui::restore();
    app_result
}